Generally, a display device is required to have a viewing angle as wide as possible so that a clear image can be seen from any visual angle. Especially, in a liquid crystal display device which has been widely used in recent years, the liquid crystal itself has viewing angle dependency. Therefore, various techniques have been developed in order to increase the width of the viewing angle.
However, in some environment, there is a case where it is preferable for a display device to have a narrow viewing angle so that only a user himself can see display contents. Especially, a notebook personal computer, PDA (Personal Data Assistant) or a mobile phone and the like are likely to be used in a place, such as a train and an airplane, where a large number of people can exist. In such a place, in view of protection of secrets and privacy, it is desirable that a display device has a narrow viewing angle so that others in the vicinity of the user cannot see display contents. As described above, in recent years, there have been increasing demands for a display device which allows switching of a viewing angle of a display device between a wide viewing angle and a narrow viewing angle according to a situation in which the display device is used. It should be noted that the demands are aimed at not only a liquid crystal display device but also any display device.
In order to meet the demands, for example, Patent Document 1 discloses a technique in which a phase difference control device is provided in addition to a display device for displaying an image. The technique disclosed in Patent Document 1 enables a viewing angle characteristic to change by controlling a voltage applied to the phase difference control device. In this Patent Document 1, a chiral nematic liquid crystal, a homogeneous liquid crystal and a randomly oriented nematic liquid crystal are given as examples of a liquid crystal mode used in a phase difference control liquid crystal display device.
Further, for example, Patent Document 2 and Patent Document 3 disclose an arrangement in which a viewing angle control liquid crystal panel is provided on a display liquid crystal panel, and these panels are sandwiched by two polarizing plates. In the arrangement disclosed in the Patent Document 2 and Patent Document 3, a viewing angle is controlled by adjusting a voltage applied to the viewing angle control liquid crystal panel. In this Patent Document 2, a liquid crystal mode of the viewing angle control liquid crystal panel is a twisted nematic mode.
Further, for example, Patent Document 4 discloses a display having a liquid crystal device, between a backlight and a display device. The liquid crystal device makes it possible to switch over between a first state and a second state, the first state providing a first viewing angle, the second state providing a second viewing angle which is narrower than the first viewing angle.
[Patent Document 1]
Japanese Unexamined Patent Application Publication Tokukaihei No. 11-174489 (published on Jul. 2, 1999)
[Patent Document 2]
Japanese Unexamined Patent Application Publication Tokukaihei No. 10-268251 (published on Oct. 9, 1998)
[Patent Document 3]
Japanese Unexamined Patent Application Publication Tokukai No. 2005-309020 (published on Nov. 4, 2005)
[Patent Document 4]
Japanese Unexamined Patent Application Publication Tokukai No. 2005-316470 (published on Nov. 10, 2005)
[Non-Patent Document 1]
Nitta Denko technical report 84 (Vol. 41), pp 26-29, 2003